This invention relates to a method of preparing microsphere composite and in particular to a method of preparing microsphere composite of collagen and bioceramic powder, the interior and the surface of the microsphere have a three dimensional network of collagen fibers.
Human bone tissue needs to be repaired as it has defects due to damages or diseases. If bone implant material is added to the defect to bear stress and provide a scaffold for cell culturing, which can effectively augment bone structures and induce bone tissue regeneration and repair. The best method to get bone implant material is autogenous implant, but this source is limited and the patient suffers a second operation. Allogenous bone graft has problems of immune response and other side effects. Therefore, the synthetic bone tissue material gives another choice. The conventional synthetic implant material has inertia in order to coexist with living tissues. But the inertia material induces fibers around the implant, therefore the implant is not fixed or the tissues around it become fibers or die. Prior arts have discovered there is biological binding between tissue and biomaterial, and the biomaterial has better biocompatibility. Collagen is the most abundant protein of bone matrix, has biocompatibility and low immune response causing property, and provides a suitable matrix for regenerated osteocyte""s anchorage. Adding bioceramic powder such as tricalciun phosphate (TCP), hydroxyapatite (HAP) to collagen forms composite material, this composite material has larger mechanical strength and further simulates the composition components of bone tissue. Such composite material can be used as carriers for cells and growth factors which induce tissue regeneration and speed up bone repair rate.
There are many shapes of implant materials such as bulk shape, cement shape, and microsphere shape. Each shape has its own disadvantages. Bulk shape bone implant has larger mechanical strength, so it is not suitably applied in various shapes of bone defect in operation. As per cement shape and microsphere shape bone implants, which can be conveniently operated, molded in accordance with the shape of the defect, and injected to the location of bone defect to reduce patient""s pain in the operation. The disadvantages of materials of these shapes are such materials can not be easily fixed at the defect and have smaller mechanical strength.
Conventional technology filled collagen in the pores of sintered porous ceramic materials via pouring or immersion. Sintered ceramics has high hardness to bear stress, but has limitation in modability. In addition, the porous ceramic is not bioresorbable and an obstacle to further growth of new bone tissues.
Prior art mixed the hydroxyapatite dissolved in acidic solution with reconstituted collagen, then adjusted the pH of the solution to slightly basic to make hydroxyapatite dispersed in collagen. Prior art also mixed hydroxyapatite precursor with collagen solution, and used acid-base reaction to convert the precursor to hydroxyapatite dispersed in collagen fibers matrix. Chu et al in 1988, 1989 (U.S. Pat. Nos. 4,776,890, 4,888,366), mixed collagen solution with hydroxyapatite powder directly to form gel solution, which has injectable advantages and applications to repair of soft tissues. The above composite material formed by direct mixing of the composition components is separated into two phases after a period of time due to appreciable specificity difference between collagen and bioceramic powder. In addition, the diameter of bioceramic powder used is about 0.5 mm which is too large, this type of bioceramic is not bioresorbable and induces fiber tissues around it. This direct mixed composite can not form similar collagen fibrous network of bone tissues providing the needed growth environment of bone tissue cells via an observation of the microscopic structure of the composite.
In microsphere composite material, collagen and bioceramic powder are distributed more homogeneously. Large amount of the microspheres can be arranged in any orientation, and this remedies nonhomogeneity of two phases of each microsphere macroscopically. In addition, the microsphere has good modability and can be prepared in injectable form to reduce the need of operation due to its small diameter. Prior art used silicon oil to prepare microsphere of collagen, then further mixed hydroxyapatite with collagen solution, the mixture was discharged into a fast agitated ethyl-2-hexyl cocoate to make collagen form sphere, the solution was centrifuged and ethyl alcohol was added to the solution to remove ethyl-2-hexyl cocoate to separate microsphere of collagen and hydroxyapatite. Wang et al in 2001 (ROC Patent Publication No. 420604) mixed collagen solution with hydroxyapatite to form a mixture solution, spherical droplets of which were discharged into an oil phase such as olive oil, the collagen of the mixture solution reconstituted to form fiber network microsphere, a cross-linking agent such as glutaraldehyde was added to the oil phase to make the reconstituted collagen link with the hydroxyapatite, finally the microsphere was separated from the oil phase. In the above process to prepare microsphere, organic solvent used might damage collagen structure, and it is worried about that residual organic oil or cross-linking agent in the prepared microsphere causes damages to tissues. In addition, more processes are needed to separate the oil phase.
The object of the present invention is to provide a method of preparing microsphere composite of collagen and bioceramic powder in order to improve the drawbacks of conventional methods to prepare composite material. The present invention uses collagen solution and reconstitution technology to prepare the microsphere composite. Collagen and bioceramic powder are distributed homogeneously in the microsphere composite, and the interior and the surface of the microsphere have a three dimensional network of collagen fibers. There is no residual organic solvent, organic oil or cross-linking agent in the prepared microsphere composite, so there is no need to worry about they may cause damages to tissues. In addition, the microsphere composite of this invention has enough mechanical strength to be used as a carrier to carry cells, coat and fix different bone growth factors to induce tissue regeneration and speed up bone repair rate. The microsphere composite can be injected in bone repair or further processed to different shapes of plate to be applied in bone repair.